Early wavefront phase modulators employ a number of discrete drivers, such as electromechanical and piezeoelectric transducers. U.S. Pat. No. 3,742,234 to Laakmann discloses various devices of this type. FIGS. 5-7 illustrate stacks of piezoelectric elements, which are deformed by applying various voltages thereto, to in turn, cause deformation of a mirror. The systems constructed in accordance with the teachings of this patent are stable to only one wavelength of visible light and are incapable of correcting fractions of wavelengths or electromagnetic radiation having shorter wavelengths than those of visible light. In contrast, the Feinleib et al. U.S. Pat. No. 3,904,274, incorporated by reference herein, teaches monolithic devices, which are far simplier to fabricate and are far more stable. Additionally, they have uniformity of the piezoelectric coefficient from point to point, since the material is formed from one wafer. Their stability produces far more accurate control, in contrast with the discrete actuators of the '234 patent.
Another device of this nature is the subject of U.S. Patent Application Ser. No. 970,055, Filed Dec. 14, 1978, in the names of Nedo Peter Albertinetti and Ralph Edward Aldrich, entitled "A Multiple Layer Peizoelectric Wavefront Modulator". The device disclosed in said patent application employs a number of layers of piezoelectric material bonded together, each layer being internally polarized in a direction opposite to the next adjacent layer. This device, in contrast with the device of the Feinleib patent, advantageously may employ driver voltages in the neighborhood of 500 volts. It is the object of this invention to maintain the low voltage advantage of the multiple layer device of the above-mentioned patent application, and yet increase the sensitivity of the device.
The bender Bi-Morph concept, which is utilized in the present invention, is a subject of an article entitled "Bender Bi-Morph Scanner Analysis" by J. J. Schaffer and D. L. Fried, published in Applied Optics, Volume 9, No. 4, dated April 1970, commencing on Page 933. As is indicated by FIG. 1 of the article, the application of an electric field across the T dimension of a two layer element will cause the lengthening of one layer and the shortening of the other to produce a bending effect, to in turn, induce tilting of a mirror element mounted upon the free end of the two layer element. In contrast with the present invention, major surfaces of the layers are not parallel to the mirror surfaces and are not clamped to a support device at opposite non-centralized portions, which produces a high mechanical advantage which is highly beneficial for use in wavefront modulators.